Nucleic acids, membranes and tissues

Epithelia

• Epithelia forms the body's outer layer and lines hollow structures.
• Epithelial tissue is characterized by cellularity, polarity, attachment, avascularity, and regeneration.
• Cellularity in epithelia means cells are closely bound by cell junctions.
• Polarity in epithelium means there is an exposed surface facing the outside or an internal space, plus a base attached to underlying tissue.
• Attachment means the base of an epithelium is bound to a thin basement membrane or basal lamina.
• Avascularity in epithelia means they lack blood vessels and get nutrients via diffusion or absorption.
• Regeneration means damaged or lost cells are continuously replaced through stem cell divisions.

Epithelial Tissue Functions

• Epithelial tissue functions by providing physical protection and controlling permeability.
• Epithelial tissue can also provide sensation.
• Some functions include producing specialized secretions.
• Ciliated epithelium functions by moving things across the surface.

Intercellular Connections

• Adhesion belts are interlocking proteins wrapping cells, forming a continuous band connecting adjacent cells.
• The terminal web is a cytoskeleton mesh near the apical surface in cells with microvilli.
• Tight junctions prevent solute passage between cells, forming a water and solute-tight seal.
• Gap junctions allow cytoplasm and signals to flow between connected cells.
• Desmosomes connect cells to other cells.
• Hemidesmosomes connect cells to the basement membrane.
• Glands are collections of epithelial cells that produce secretions.
• Endocrine glands release secretions directly into the interstitial fluid.
• Exocrine glands release secretions into a duct.
• Apocrine secretion involves the loss of part of the cytoplasm during the release of secretory materials.
• Merocrine secretion involves vesicles releasing at the apical surface.
• Holocrine secretion involves gland cells bursting to release contents.
• Simple epithelia consist of single layers of squamous, cuboidal, or columnar cells.
• Stratified epithelia consist of multiple layers of squamous, cuboidal, or columnar cells are stacked.
• Pseudostratified ciliated columnar epithelial cells have cilia for movement and protection.

Connective Tissue

• Connective tissue is located throughout the body but is never purposefully exposed to the outside environment.
• Connective tissue components are specialized cells, extracellular protein fibers, and ground substance.
• General functions of connective tissue are establishing structural fragments of the body, protecting delicate organs, supporting surrounding tissues/connecting other tissue types, transporting fluids/dissolved materials, storing energy reserves, and defending against microorganisms.
• Connective tissues are classified into connective tissue proper, fluid connective tissue (blood/lymph), and supporting connective tissues (bone/cartilage).
• Matrix is the extracellular substance in which the tissue cells are embedded.
• Loose connective tissue supports and cushions delicate structures like blood vessels, the liver, and nerves.
• Areolar tissue separates skin from deeper structures and contains elastic fibers that allow the skin to stretch.
• Adipose tissue contains mostly adipocytes in deep skin layers that pad areas, such as the eyes and kidneys.
• Reticular tissue provides structure for organs.

Dense Connective Tissue

• Dense connective tissue is made of fibers, making it stronger than loose connective tissue.
• In regular dense connective tissue, fibers run in the same direction.
• In dense irregular connective tissue, fibers form a mesh.

Connective Tissue Proper

• Permanent resident cells are always present:
• Fibroblasts produce proteins and polysaccharides. --They form proteoglycans, which makes ground substance viscous. --Fibrocytes are the protein fiber producers.
• Adipocytes are dominated by a large lipid droplet, "Fat Cells". -- They come in variable numbers.
• Mesenchymal cells are stem cells that can become any cell.
• Melanocytes are found and produce melanin.
• Transient cells move depending on where they are needed, and are not always present.
• Macrophages are "big eaters". --They engulf damaged cells or pathogens. ---They are a rare form of cell but are very important ---Activation can activate the immune system as well as other macrophages, plus releases cytokines that trigger the attraction of other immune cells, as well as fever and inflammation ---Fixed forms stay in place. ---Free forms wander the body. --Mast cells are small mobile cells that release histamines. --Lymphocytes remembered immunity --Microphages: Another phagocytic cell type
• Fibers are:

1. Collagen fibers are long, straight, and flexible with more tensile strength than steel and make up most tendons.
2. Reticular fibers form mesh patterns in all directions and stabilize organs and blood vessel positions.
3. Elastic fibers stretch and return to original shape.

Cartilage

• Supporting connective tissue has solid matrix
• Cartilage is a firm gel with fibers called chondrocytes.
• Chondrocytes grow in “Lacuna,” pockets within the matrix.
• Chondroblasts (perichondrial cells) play an important role in cartilage formation. --They also produce new matrix. --Perichondrium has connective tissue protecting cartilage --Appositional growth a type of which helps areas larger --Interstitial Growth: When the chondrocyte undergoes mitosis inside the lacuna which is rare and slow, This is why cartilage wounds take so long to heal. --Hyaline provides inflexible support. ---Ex.) Synovial cartilage and fluid in your knee cap --Elastic withstands distortions while returning to the original shape. --Elastin resists compression. -----Ex.) Knee meniscus
• Osteocytes: Bone cells. Matrix has extremely strong and flexible fibers that support the cells.
• Tissue Membranes have four types

1. Mucous membranes line body cavities and canals leading to the body's outside a ) Lines surfaces to facilitate absorption b.) Ex.) esophagus, trachea, reproductive organs
2. Serous membranes line cavities not connective to outside. a.) Made of squamous cells of membrane outside b. )Translate lubricates moving surfaces c.) Example pericardium between lungs/heart
3. Cutaneous Membrane is exposed to outer enviroment a) Cover dead defending cells . Ex .) skin
4. ) Synovial Membrane are lined with free cavities in knees, elbows, and shoulders </existing_notes>

Study of nucleic acids, cell membranes, epithelia, and connective tissues. Includes the structure of DNA and RNA as well as the function and protein synthesis. Covers coding and non-coding regions of DNA.